Sea Lion can be criticised on its own planning assumptions without using Overlord as the standard of comparison. Waiting off the British coast for the tide to fall would expose barges and troops to coastal artillery. Dover adds a long-established garrison and successive layers of fortifications, including older earthworks that could still obstruct an assault. Driving an R-class battleship into a captured port to wreck its facilities is a desperate last resort in this scenario, after Southampton, Portsmouth and Dover have fallen.
Notable Point · 4:03:23-4:07:50
Sea Lion's landing barges and Dover's defences
Sea Lion's proposed barge landings face tidal delays, exposed unloading and fortified ports before the invaders can establish an army ashore.